Since photographic material is generally composed of a support having an electric-insulating property and photographic layers formed thereon, an electrostatic charge is frequently accumulated on the photographic material by the contact friction of the surface thereof with the surface of the same kind of photographic material or a foreign material. An electrostatic charge can also be accumulated by the separation of the surface thereof from the surface of the same kind of photographic material or a foreign material during the production thereof or during use. The accumulated electrostatic charge causes various problems the most serious of which is that the accumulated electrostatic charge is discharged before development. This discharge partially exposes the photosensitive silver halide emulsion layers of the photographic material. This partial exposure results in forming dot-like spots or branch-like or feather-like spots after development of the photographic material. These spots or so-called static marks greatly reduce the commercial value of the photographic film. The problems resulting from the formation of static marks on medical or industrial X-ray film are apparent. The occurrence of this phenomenon creates an addition problem since the occurrence of the phenomenon cannot be confirmed prior to development of the photographic material. Furthermore, the accumulated electrostatic charge induces secondary problems such as attaching dust onto the surface of the photographic film and making it difficult to uniformly coat photographic layers on the support.
An electrostatic charge, as described above, is frequently accumulated during the production and use of photographic materials. For example, an electrostatic charge is created by frictional contact between a photographic film and rollers during the production step for the photographic film or by the separation of the support of a photographic film from the silver halide emulsion layer surface thereof during the winding or rewinding process of the photographic film. Furthermore, an electrostatic charge is created by the contact friction of an X-ray film with a mechanical part or a fluorescent intensifying screen in an automatic X-ray camera, and by the contact friction of a photographic film with a packaging material. The occurrence of the static mark of a photographic material induced by the accumulation of such an electrostatic charge becomes increasingly serious as the sensitivity and processing speed of the photographic material increase. In recent times, photographic material is frequently subjected to severe processings such as high sensitization and high speed coating of photographic material, high speed photographing, high speed automatic processing. Accordingly, the static mark is more likely to form.
In order to remove problems created by the electrostatic charge, it is preferable to add antistatic agents to photographic materials. However, antistatic agents generally used in other fields than photography cannot always be used as the antistatic agents for photographic materials. Furthermore, there are various restrictions specific to photographic materials about the antistatic agents which are used for photographic materials. In addition to possessing excellent antistatic properties, the antistatic agents used in photographic materials must not give bad influences on the photographic properties of photographic materials, such as the sensitivity, fog formation, granularity, sharpness. Furthermore, the agents must not have: bad influences on the film strength of photographic materials (i.e., the photographic materials containing the antistatic agents are not readily scratched when rubbed together or scraped with solid materials); or bad influences on the adhesive property of the photographic materials (i.e., the photographic materials containing the antistatic agents do not readily stick to each other or to the surfaces of foreign materials). Furthermore, the agents must not accelerate fatigue of processing solutions for photographic materials or reduce the bonding strength between the photographic layers of the photographic materials. Thus, there are many restrictions with respect to the application of antistatic agents to photographic materials.
In accordance with one method for eliminating problems created by electrostatic charge, the electric conductivity of the surface of a photographic material is increased so that the electrostatic charge flees in a short period of time before the charge is accumulated and discharged.
There have been prior attempts to improve the electric conductivity of the supports for photographic materials and various coated surface layers and the utilization of various hygroscopic materials or water-soluble inorganic salts. These attempts involve the use of certain kinds of surface active agents, polymers. For example, there are the polymers as described in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716, 3,938,999, etc.; the surface active agents as described in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, etc.; and the metal oxides and colloidal silicas as described in U.S. Pat. Nos. 3,062,700, 3,245,833, 3,525,621, etc.
However, these materials show a different specificity for different kind of film support or different photographic composition. Therefore, some materials described above give good results for specific film supports and photographic silver halide emulsions or other photographic constituting elements. However, they are not only useless for static prevention of other film supports and photographic constituting elements but have bad influences on photographic properties.
Other materials possess an excellent antistatic effect but cannot be used for photographic materials because they have bad influences on photographic materials such as the sensitivity of photographic silver halide emulsions, the formation of fog, granularity and sharpness. For example, it is generally known that polyethylene oxide series compounds have an antistatic effect. However, they frequently have bad influences on the photographic properties, such as the increase of fog, the desensitization and the deterioration in granularity. Particularly, in a photographic material having photographic silver halide emulsion layers coated on both sides of a support as a medical direct X-ray photographic film, it has been difficult to establish a technique of effectively creating an antistatic property without having bad influences on the photographic properties.
As described above, the application of antistatic agents to photographic materials frequently encounters various difficulties and the applicable range is limited.
According to another method of eliminating the problems on photographic materials caused by electrostatic charge, the static potential of the surface of a photographic material is controlled. This minimizes the generation of static electricity by friction or contact as described before.
For example, attempts have been made which utilize fluorine-containing surface active agents as described in British Pat. Nos. 1,330,356 and 1,524,631, U.S. Pat. Nos. 3,666,478 and 3,589,906, Japanese Patent Publication No. 26687/77 and Japanese Patent Application (OPI) Nos. 46733/74 and 32322/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). However, since the electrostatic characteristics of the photographic materials containing these fluorine-containing surface active agents utilize the characteristics of surface active agent, such as a monomolecular film formation, etc., they are greatly dependent upon the conditions for producing these photographic materials. Therefore, it is very difficult to produce stable photographic products having constant quality and constant electrostatic characteristics. For example, the electrostatic characteristics of photographic materials produced change greatly dependent upon temperature and humidity during the coating of photographic layers on supports, as well as temperature, humidity and drying time during drying of the photographic materials after coating. Photographic products having good properties are obtained under certain conditions but photographic materials having very inferior electrostatic characteristics are formed in other cases. This creates a serious problem with respect to quality control. The fluorine-containing surface active agents are inferior in that even if the photographic materials containing these surface active agents have good electrostatic characteristics immediately after production, the electrostatic characteristics become inferior with the passage of time.
In an attempt to overcome the difficulties caused by the use of these fluorine-containing surface active agents, fluorine-containing polymers have been used in photographic materials. These attempts involve the use of homopolymers or copolymers of the acrylic acid esters or methacrylic acid esters of fluorine-containing alcohols as described in British Pat. No. 1,497,256; the use of copolymers prepared by copolymerizing the aforesaid fluorine-containing monomers and a monomer having a polyethylene oxide chain as described in Japanese Patent Application (OPI) No. 158222/79; the use of copolymers prepared by copolymerizing the aforesaid fluorine-containing monomers or such fluorine-containing monomers as the vinyl esters of fluorine-containing carboxylic acids, fluorine-containing vinyl ethers, fluorine-substituted olefins, etc., with a monomer having quaternary nitrogen as described in British Patent No. 1,535,685; or the use of interpolymers prepared by interpolymerizing the maleic acid esters of a fluorine-containing alcohol, maleic acid, and other monomer.
By using these fluorine-containing polymers in a photosensitive material, some control of the electrification voltage on the surface of the photosensitive material can be achieved, and the generation of static charge due to friction or contact with other materials can be reduced to some extent. The polymers offer some solution to the problems with the aforementioned fluorine-containing surfactants, i.e., great dependence of the electrostatic characteristics on process conditions, and their degradation with time. However, the photo-sensitive material containing these fluorine-containing polymers is still unsatisfactory in electrostatic characteristics and its photographic properties and the physical properties of the film that are important factors of photosensitive material are not as good as desired. These problems reduce the commercial value of the photosensitive material greatly, and it is practically impossible to use these polymers in a photosensitive material. For example, layers in a photosensitive material incorporating an emulsion of the fluorine-containing polymer described in British Patent No. 1,497,256 are so sticky that the emulsion layers in two such photosensitive materials easily adhere to each other, or the emulsion layer in one photosensitive material adheres to the backing layer of an adjacent photosensitive material. The two layers cannot be separated from each other at all, or a readily visible bare patch appears upon pulling them apart. In addition, scars are easily formed in layers in the photosensitive material incorporating these polymers when they are abraded or scratched by another material. All of these problems can reduce the commercial value of the photosensitive material considerably. Japanese Patent Application (OPI) Nos. 158222/79, 129520/77 and Japanese Patent Publication No. 23828/74 also disclose a fluorine-containing polymer, but when it is incorporated in a photosensitive material, its ability to control electrification voltage is so low that it must be contained in the photosensitive material in high proportions. Not only does this increase the production cost but it also affects adversely the photographic characteristics (e.g., reduced sensitivity and density as well as increased fogging) and the physical properties of the film (e.g., vulnerability to scratches). Therefore, it has so far been impossible to use these polymers in photosensitive materials.